1. Field of the Invention
This invention concerns controllers, more particularly electrical switch controllers that permit a single electrical load (such as a light) to be controlled by multiple switches.
2. Background Information
It is frequently desirable to control an electrical load—such as a light or a fan—with more than one on/off switch. For example, in a large room with three entrances—such as an auditorium, a warehouse, or a stadium—it would be useful to have three light switches—one at each entrance—to control the lighting for the room.
FIG. 1 shows two conventional wiring methods for a circuit system that allows three switches to control a load. In both cases, two entrances would use a “3-way switch” and one entrance would use a “4-way switch.” (Such switches are more complicated and expensive than “single pole” switches that are used when a load is controlled by just one switch.) In these conventional wiring methods, each time a user moves any switch from one position to another (e.g., from down to up or up to down), the state of the light changes (e.g., goes from off to on or on to off). In these conventional methods, standard wire would be used to make electrical connections in at least five segments of the circuit:
(1) from an A.C. HOT terminal to a first 3-way switch;
(2) from the first 3-way switch to the 4-way switch;
(3) from the 4-way switch to the second 3-way switch;
(4) from the second 3-way switch to the light; and
(5) from the light to an A.C. NEU terminal.
In a large room, each segment can be quite lengthy; the longer the segment, the more wire must be used and the more labor is required for installation, and thus the more expensive it is to install the circuit. In addition, for safety, the wire in each segment must be “rated” to carry the full load in the circuit. In the U.S., where electrical systems generally use 120 VAC (120 Volts alternating current), relatively heavy 12-gauge wire would typically be used throughout the circuit. Using 3- and 4-way switches is also more expensive than using single-pole switches.
More complex known circuits that permit multiple switches to control a single load are described in U.S. Pat. Nos. 3,629,608 (“Remote Control Circuits”); 4,525,634 (“Alternating Current Switching Device”); 3,697,821 (“Light Dimming System Having Multiple Control Units”); and Re. 33,504 (“Wall Box Dimmer Switch with Plural Remote Control Switches”). But these circuits largely make use of relatively expensive materials.
Using semiconductor devices can entail using less-expensive materials. It is known that semiconductor devices, which are powered by DC, can be coupled via optical isolators to triacs that control AC loads. For example, U.S. Pat. No. 4,594,515 describes multiple switches (designated “LAMP ON,” “LAMP OFF,” “FAN LOW,” “FAN OFF,” AND “FAN HIGH”) that control multiple loads (lamp, fan low-speed, and fan high-speed). But this patent does not disclose using semiconductor devices that permit multiple switches to control a single load. PCT Application No. WO 97/22956 describes a circuit for controlling a single device with multiple switches connected in parallel through a microcomputer. But this is a relatively complex and expensive circuit.
It would be advantageous to provide a relatively simple device for controlling a single load with multiple switches that can use less-expensive materials and that requires less labor to install.